Question: $ { \left[\begin{array}{rrr}{1} & {-1} & {-2} \\ {-2} & {0} & {0}\end{array}\right]+\left[\begin{array}{rrr}{-1} & {-1} & {-1} \\ {0} & {4} & {2}\end{array}\right] = {?} } $
Answer: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rrr}{1}+{-1} & {-1}+{-1} & {-2}+{-1} \\ {-2}+{0} & {0}+{4} & {0}+{2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{0} & {-2} & {-3} \\ {-2} & {4} & {2}\end{array}\right]}$